The Aboriginals had a civilisation, that was the most advanced compared to anywhere else around the world for a very long time. Sure it was crude in many ways, but still far ahead of the rest. Isolation was its downfall as stagnation set in and they became lost in time. Think of them as Gardeners: where they 'terraformed' the Bush into a Parkland. Where they only used 20% of their time hunting/gathering, the rest was for ceremonial and other expressions of culture.
The original 'native' Britons were all but wiped out by the invading Germanics - systematic genocide right from the word go. Even today, barely 0.1% in the modern gene pool can be traced back to the original inhabitants.
Now that's an Indigenous Minority !
Regarding the Aboriginals not being a 'civilisation'? The majority of other civilisations that rose up 20,000 years later were 'settled' Agricultural along major river systems and any 'belief' systems were based upon the 'natural' world (Weather, Land, Harvest) of which they depended upon. The ability to travel along the Rivers to trade and stimulate further growth was there as an opportunity.
IRAQ (Persia) was probably the best example and that's where SUMER eventually kicked off.
The problem of the Aboriginals was that although they migrated early and very far, which is where they gained a lot of 'cultural' stimulation, they eventually fell into Australia - which then not only became a 'dead end', but cut them off before they could learn any major cultural advancements in 'water craft' of any major sea-going effort.
As far as 'Tracking' methods, they are the best in the world - better than the San Bushman. As far as Botany, they have the most extensive. As far as 'Breeding' combinations to prevent 'in-breeding', they have the most complex. They manipulated the natural environment to provide food, rather than the need to 'destroy' it.
One only has to remember how the Nipponese (Japs) suffered from the 'isolationism' that they brought upon themselves.
The Aboriginal 'civilisation' was still in much better shape in 1788, than when the Britons were when the Romans set foot in those Isles. It took over 500 years before the first Briton (Anglo-Saxon) managed to live in a 'House' at a time when there was no 'hostility' from the Romans upon the forest dwelling, animal fur-wearing, stick-shelter locals.